The Packers are 4th. in the league in "big plays" as defined in the following link, i.e., +10 yard run plays and +25 yard pass plays. Note the Packers are tied for 2nd. in +25 yd. pass plays with 13. That works out to 2.6 per game.
Interestingly, if one looks at the 2014 query in that link, it was 34 pass plays of +25 yards, for an average of 2.1 per game. There seems to be a tendency to remember the 50+ point scoring romps while forgetting the difficulties in getting downfield against 2-high safeties much of the rest of the time.
The combined run/pass big play percent-of-snaps for 2015 is 10.26%; for 2014 it was 10.09%.
http://www.sportingcharts.com/nfl/stats/team-big-play-statistics/2015/
Red Zone TD %: 2015 = 61%, 2014 = 57%
3rd. Down Conversions: 2015 = 38.3%; 2014 = 47.2%
http://espn.go.com/nfl/statistics/team/_/stat/downs/sort/thirdDownConvPct
http://espn.go.com/nfl/statistics/team/_/stat/downs/sort/thirdDownConvPct/year/2014
This season's 3rd. down conversion rate is remarkably low for a QB completing 71% of his passes. For perspective, a 10% differential in conversion on a typical 10 possession day equates to one extended possession, which is not a huge thing, but it is not a small thing either.
Whatever issue one finds with the offense this season vs. last, it's less a matter of big plays as it is ball control conversions.
It's interesting to look at Cobb's stats. In 2015, he was Mr. First Down, averaging 4.4 per game, gaining a first down on 56% of his targets. This season, his first down rate has dropped to 3.4 per game with his target rate up slightly (about 0.5 per game). His yards per catch is way off last season's. Whether it's the shoulder, the pressure of the contract, the pressure of being elevated to #1, getting more attention in Nelson's (or even Adams') absence, or some combination of those factors, I'll leave that as a matter of debate.
Taking a step back, it's worth noting the Packers struggled to score in 1/2 of their road games last season, so the SF game is hardly a year-over-year outlier, and it was known the Rams had a pretty decent defense coming in.
So, relax. When Adams gets back on the field and if Cobb can be a bit more productively involved, the current concerns will fizzle if they were not a little misguided in the first place.